Acoustic diaphragm with flexible rim portion and rigid body portion



J. BBRENNAN ACOUSTIC DIAPHRAGM WITH FLEXIBLE RIM PORTION AND RIGID BODY PORTION Jan.'6, 1953 Filed Feb. 20, 1947 W ly/gi oa Patented Jan. 6, 1953 ACOUSTIC DIAPHRAGM WITH FLEXIBLE RIM PORTION AND RIGID BODY POR- TION Joseph B. Brennan, Cleveland, Ohio Application February 20, 1947, Serial No. 729,846

This invention relates to acoustic diaphragms and method of making the same and more particularly to the manufacture of flexible fibrous diaphragms of the type used in loudspeakers.

One of the objects of the invention is to provide an acoustic diaphragm and a method of making the same in which the diaphragm is formed by a plurality of spaced strands or cords extending radially across at least the rim portion of the diaphragm and connected by a layer or sheet of felted fabric. In this construction the strands contribute the major part of the supporting bonded together and bridged by a relatively thin layer or sheet of felted fibrous material.

Still another object is to provide a method of making diaphragms in which strands or cords of fibrous material are first placed over a form and fibrous material is then deposited on the strands and on the form to bond to the strands and to bridge the spaces between thestrands. Preferably the strands are initially held in position over the form by looping them about pins adjacent the periphery of the form.

g The above and other objects and advantages of the invention will be more readily apparent from the following description when read in connection with the accompanying drawing, in which- Figure l is a face view of a diaphragm embodying the invention;

Figure 2 is an enlarged partial section on the line 22 of Figure 1;

Figure 3 is a view similar to Figure 1 of an alternative arrangement;

Figure 4 is a side view of the diaphragm of Figure 1;

Figure 5 is a diagrammatic view illustrating the method of forming the diaphragm of Figure 1;

Figure 6 is a view similar to Figure 4 illustrating an alternative arrangement of the strands;

Figure 7 is a top plan view of a form illustrating one manner of arranging the strands thereon; and

Figure 8 is a view similar to Figure 2 of an alternative construction.

According to the present invention diaphragms of the type generally used in loudspeakers are constructed with a supporting structure of cords or strands extending generally radially across the diaphragm and connected and bridged by a rela- 2 Claims. (Cl. 181-32) tively thin layer or sheet of felted fibrous material. As shown, in Figures 1 and 4, the diaphragm may comprise a generally circular body having a conical body portion in terminating in a central flange portion H for connection to the driving coil of a speaker and having a peripheral flat rim portion 12 by which the diaphragm is mounted. The diaphragm is formed by a plurality of cords or strands l3 which are preferably of fibrous material such as pulp fibers, cotton fibers or similar vegetable fibers or mixtures thereof formed into elongated strands. The strands may if desired be loose cards or rovings or where greater strength is required without increasing the thickness, they may be twisted or woven into relatively hard cords. The strands extend diametrically across the diaphragm, each strand extending from one edge portion of the diaphragm diametrically to the opposite edge portion. The cords are spaced substantially uniformly and are connected and bridged by a relatively thin layer of felted fibrous material M. This material may be of sufficient thickness and density to connect and bridge the fibers so that a complete diaphragm will be formed and are sufficiently thin to be extremely flexible.

The completed diaphragm may be mounted in the usual manner by clamping the rimportion l2 to a support so that the main body portion 110 can vibrate in response to the driving coil. It will be noted that when the diaphragm is mounted the cords or strands l3 provide the major supporting strength so that the felted layer or sheet H can be relatively thin and weak. In this way a diaphragm having high strength and an extreme degree of flexibility is produced.

Instead of running the strands or cords diametrically across the diaphragm as shown in Figure 1, they may be arranged in parallel groups which cross each other as shown in Figure 3. This construction provides a diaphragm which is reinforced by crossing cords in its central portion to provide greater strength and'rigidityof the central part of the conical body I0 while leaving the rim portion highly flexible. As shown in Figure 3, there are three groups of cords I5 of sufficient width so that each group of cords will occupy approximately one-sixth of the rim circumference at each end with the several groups arranged at angles with respect to each other. The cords are bonded together and have the spaces between them bridged by felted fibrous material such as the material I 4 of Figure 2 to complete the diaphragm.

Still another arrangement of cords is shown in Figure 6 wherein there are a plurality of main cords l6 extending radially across the diaphragm and each of which has connected thereto at spaced points in its length secondary cords H. In this construction the main cords 16 extend radially of the diaphragm and the secondary cords lie at angles to the main cords so that they extend ,igenerally radially across rat'least the' 'rim portion *of the *diaphragm- This arrangement provides a diaphragm of substantially uniform thickness and strength throughout. It will Jo'e understood that cords l6 and-Hare connected together and are bridged byilted fibfousmaterial such as shown at M inFigure'2.

In forming diaphragms according to the present invention the cords or strands are first"-laid over a porous form and fibrous material lis deposited thereon by spraying or from aliquidsuspension as desired. Figures and 7'-illustrate one apparatus for forming diaphragms including "a porous :form 118 having substantially the -con'- -figuration of a :desired finished -.diaphragm. "The form l8is supported :on'a suction box -19 which may besconnectedto a source of vacuum through :a-"conduit --2 I andrmayhavean upstanding flange -33 around its periphery to receive :a liquid vsuspension 0f fibrous :material. A plurality, of spins are arranged around the periphery-ofgthe r form beyond the portion thereof which defines theaedge of thediaphragm. In usingthis. apiparatus a continuous cord-=01 strand =24 aasbest z'seenin :Figure '7 mayxbe looped-over the pins so "thatithe cord orstrand will extend across and 'li'eagainst' the form. Thecordls may ibearranged "diametrically as :shown Figure '7 for could if desiredffollow the arrangement of Figure 3. -As

"the v cords are 1: placed, the "central parts thereof :.-:may be forcedinto the bottom cuprportioniof :the 'form and may, if :necessary, lbes'held therein by tying-orrclamping. :Since the bottom :en'dof ":the 5011p will :be icu't out the completed "diaaphragm, it will be seen that =any desiredholding :means employed :for the cords at this point will :notzafleet the finished diaphragm.

':density and?the desired finished-shape. sAfter trimming'ithe edge and cutting iout :the :center ol the f cup shaped portion, rthe :diaphragm is compl'eted-andtready I for use.

acompleted diaphragm "the'lsec'tion :rnay

be a'sis ho'wn inzFigure 2 in which the diaphragm :has a ;greater ithickness as at "points where-the 'rcordsoccur or. may, if preferred, be 20f uniform thickness asshown i-n Figure 8. In :this figure thedesired density.

"While several embodiments of the invention have been shown and described in detail herein, it will b'e understood that they are illustrative only and are not to be taken as a definition of "the scope of the'invention, reference being had sfor this :purpose to the appended claims.

What is claimed is:

1. An acoustic diaphragm having a concave bodyportionandaperipheral,mountingrim-portion extending laterally :ofthe body. portion. said bodyandrim portions formed by a .plurality'of separate flexible elongated figbrous strands extending igenerally radially across :the rim *and body portions and circumferentiallyrspacecl from 1 each other, and a relatively thin %sheet of felted fiibrous material inclosing and bonded to the .strands in the rim and :body portions and tbridging the spaces bet-ween them, the flexible strands reinforcing the body :portion and imparting fiexibility to the rim portion.

2. acoustic diaphragm :having :a "concave body portion and aperipheral, mounting-rimgp'or- :tion extending laterally of the body portion-said :body and rim portions =formecl=by "a plura'li ty -of separate flexible elongated fibrous strands -ex tendingsgenerally radiall :fromthewcentr'al apart #of the bodyportion a'cross the :rimportion, and

circumferentially spaced from -.each other, and ri-relatively thin'shee't ofielt'ed fibrous material inclosing and bondedtothestrands inthe :and body portions ancl -bridging the :spaces *bei-tweenithem, the -flexible=strands 'reinforcing the bodyyportion andimparting flexibility to therim gportion.

JOSEPH B. L'BRENNAN.

file o'f' this patent:

UNITED STATES PATENTS 

